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Overall, U.S. airlines' on-time rates improved over August, but dropped from September 2011

American Airlines had the lowest number of on-time arrivals of any airline this September, according to the U.S. Department of Transportation's Air Travel Consumer Report released Thursday. Only 58 percent of American flights arrived on time and 3.1 percent of its flights were canceled.

Weather is the most common cause of delays for carriers. Factors within the airline's control, such as maintenance and crew problems, are the second most common cause.

In the case of American Airlines, factors within the airline's control were the primary cause of the exorbitant delays. The bankrupt airline has had long, drawn-out negotiations with pilots over their contracts, and its relationship with maintenance and ground crews is strained because of layoffs and pay cuts.

During the September delays, American management accused its pilots of intentionally delaying flights by calling out sick or writing up last-minute maintenance issues to protest new work and pay rules imposed by the airline.

"There is no sick out. The union does not condone it," said Captain John S. Diacsuk, an American Airlines pilot who has flown for the airline for over 23 years.

American announced earlier this week that it would attempt to make up for its poor performance this fall by offering double elite qualifying miles for any flight flown in November and December this year.

On September 30, a flight from Boston to Miami was forced into an emergency landing at New York's JFK airport when a row of seats became unbolted during flight. A second incident occurred the following Monday evening, prompting American to ground eight planes as it further investigates the cause of the safety issues.

The FAA replied to an inquiry into the cause of the maintenance issue stating, "preliminary information indicates that a row of three seats in the coach cabin apparently became loose. Three passengers were accommodated in other seats before the aircraft landed safely at JFK."

The FAA also previously announced in August that it was seeking up to $162 million in fines from American for safety violations and had placed American under close scrutiny following its declaration of bankruptcy last November.

Overall, U.S. airlines' on-time arrival rates improved over August, but were lower than September of the previous year. The number of monthly consumer complaints varies in proportion to the number of on-time arrivals, proving delayed flights equal unhappy fliers.

ExpressJet Airlines was second in line for the worst on-time performance with 81 percent of flights arriving on time, followed by United Airlines with 82 percent of on-time arrivals.

On the other hand, 96.4 percent of Hawaiian Airlines flights arrived on time making it the most punctual domestic airline, followed by AirTran (90.9 percent) and Delta (89.7 percent).